1. Field of the Invention
The present invention relates generally to a WiMAX system analyzer having a Radio Access Station (RAS) emulation function and a method of acquiring Uplink (UL) synchronization and testing a Portable Subscriber Station (PSS) using the WiMAX system analyzer, and, more particularly, to a WiMAX system analyzer having an RAS emulation function, which is equipped with the RAS emulation function, thereby being capable of acquiring and analyzing the UL synchronization of a PSS without requiring that a separate test function be provided to the PSS, and a method of acquiring UL synchronization and testing a PSS using the WiMAX system analyzer.
2. Description of the Related Art
Currently, methods of wirelessly accessing the Internet include a method of accessing the Internet via a mobile telephone network based on a Wireless Application Protocol (WAP) or Wireless Internet Platform for Interoperability (WIPI) platform, and a method of accessing the Internet via a public wireless Local Area Network (LAN) or an Access Point (AP). However, the method using a mobile telephone network has fundamental limitations on use as a universal Internet access method due to the limited screen size, the limited input interface, and a billing system based on a measured rate system. Meanwhile, the method using a wireless LAN has fundamental problems in that it can only be used within a range having a radius of tens of meters around an AP, and in that it also realizes poor mobility. In order to overcome such problems, ‘portable Internet service’ (WiMAX, or WiBro, which is a subset of mobile WiMAX and a Korean portable Internet standard) has been proposed as wireless Internet service capable of enabling high-speed Internet access at ADSL-level quality and cost, either when at rest or in intermediate-speed motion.
FIG. 1 is a diagram illustrating a method of allocating resources along a time axis and a frequency axis in Orthogonal Frequency Division Multiple Access (OFDMA). In general communication systems, since radio resources, that is, time and frequency, are limited, they must be allocated to a plurality of PSS users and used by them. Meanwhile, unlike existing CDMA-based systems and Wireless LAN (WLAN) systems, WiMAX systems employ OFDMA, in which a two-dimensional resource region, defined by the time axis and the frequency axis, is allocated to respective PSSs, as shown in FIG. 1.
FIG. 2 is a diagram showing the MAP structure of a WiMAX system. As shown in FIG. 2, in the WiMAX system, a plurality of pieces of data using the same channel coding method and modulation method is sent in a batch in order to improve efficiency. A set of data regions using the same channel coding method and modulation method is referred to as a “burst.” The location and size information of each burst can be seen from the MAP information of a frame, as shown in FIG. 2. Here, the term ‘frame’ refers to a structured data sequence having a fixed duration, which is used in the Physical Layer (PHY) standard. A single frame may include both Downlink (hereinafter abbreviated as “DL”; a link from an RAS to a PSS) and Uplink (hereinafter abbreviated as “UL”; a link from a PSS to an RAS) sub-frames.
Since the WiMAX system employs TDD, in which UL transmission and DL transmission share the same frequency but are performed at different times, essential information, including the length of a single frame and the ratio of a DL section to a UL section, is provided via MAP information. In order to dynamically allocate resources to PSSs, an RAS may send different MAPs through each frame. In this case, a MAP may be divided into DL_MAP, containing DL transmission information, and UL_MAP, containing UL resource access authority. Here, DL_MAP can be defined as a Media Access Control (MAC) layer message that defines the symbol offset and sub-channel offset of a burst divided and multiplexed along the subchannel and time axes on a downlink by an RAS, and the numbers of symbols and sub-channels, that is, allocated resources. A frame number having a value varying depending on the frame is included in the DL_MAP. Next, the UL_MAP may be defined as a set of pieces of information that completely defines the access to a UL section. UL_MAP may include Connection Identifier (CID) information. Furthermore, a uniquely defined preamble is present in the first symbol of a DL sub-frame, by which the PSS can be made aware of the start point of DL transmission. Furthermore, a cell Identification (ID) information and segment information are included in the preamble.
Meanwhile, if the frame number of a DL signal does not increase, the PSS loses synchronization, so that a DL sub-frame having an increasing frame number needs to be provided in order for the WiMAX system analyzer to analyze the performance of the PSS. As a result, in order to acquire and analyze UL synchronization via the WiMAX system analyzer, the help of the RAS is inevitably required. However, there are problems in that it is not easy in practice to use the RAS to test the PSS and in that the cost of establishing an analysis environment for the test is high.
Of course, if the PSS is equipped with a predetermined test mode (PHY mode), for example, a function of creating a UL sub-frame without requiring a network entry process in conjunction with the RAS when a CID, previously assigned thereto and stored therein, is received, a function of not performing error processing even though the frame number of a DL sub-frame does not increase, or a function of generating a trigger signal, indicating the start of a UL sub-frame when outputting the UL sub-frame, the help of the RAS is not required. However, there is a problem in that analysis itself is impossible if a PSS manufacturer does not provide the test mode, and there is inconvenience in that different interfaces must be managed for respective manufacturers when the respective PSS manufacturers provide the different interfaces, even if the PSS manufacturers provide such test modes.